Method of fabricating semiconductor device with water protective film

ABSTRACT

A semiconductor device includes an interlevel film constituted by a first dielectrics film containing dangling bonds and a bonded group of Si and hydrogen, and a second dielectrics film formed on the first dielectrics film.

This is a divisional of application Ser. No. 08/005,670, filed Jan.19,1993, U.S. Pat. No. 5,376,590.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor device and a method offabricating the same and, more particularly, to a semiconductor devicehaving a multilevel interconnection formed on a semiconductor device anda method of fabricating the same.

In a multilevel interconnection technology performed on a semiconductordevice in order to increase the packing density of a semiconductorintegrated circuit, planarization of an interlevel film is a veryimportant factor, and a number of dielectrics film formation methodshave been developed. A representative method is a sol coating method(spin on glass) by which planarization can be easily obtained. Also,ozone TEOS (tetraethoxysilane) CVD making use of a chemical reactionusing TEOS and ozone as materials has been put into practical userecently.

It is, however, known that in these methods, a large amount of water iscontained as a reaction product in a film.

On the other hand, as a drain electric field is increased due tominiaturization of MOSFETs, a hot-carrier tolerance has become a majorproblem in device reliability; carriers acquiring a high-energy state(becoming hot) in a high electric field are injected into a gate oxidefilm and trapped inside the oxide film or generate an interfacial levelbetween the gate oxide film and a substrate, thereby degrading thedevice characteristics. It is known that if a large amount of an OHgroup is present in the gate oxide film, the degradation in devicecharacteristics caused by hot-carrier injection is increased.

A dielectrics film formed by the spin on glass or the ozone TEOS(tetraethoxysilane) CVD (chemical vapor deposition) contains a largeamount of water. If this water diffuses to a gate oxide film, an OHgroup is formed in the gate oxide film, and this may accelerate devicedegradation by hot carriers. Therefore, the use of a dielectrics filmformed by these methods as a monolayer film is unpreferable in devicereliability. Conventionally, as a method of forming these dielectricsfilms not directly on an interconnection, a method of formingdielectrics films by using glow discharge plasma CVD has also beendeveloped. However, such a film is formed not for the purpose ofpreventing device degradation but as a protective film for preventing aninterconnection degradation caused by the film formation temperature orimpurities in the film. Actually, a first interlevel film was formed inthis manner, and a first metal interconnection was formed on a MOStransistor device. Subsequently, a dielectrics film according to theplasma CVD as a second interlevel film, a film according to the ozoneTEOS-CVD, and a dielectrics film according to the spin on glass wereformed in this order to constitute a multilevel dielectrics film. Afterannealing was performed, film formation was again performed by theplasma CVD. In addition, holes are formed in this second interleveldielectrics as connection holes with respect to a second metalinterconnection, and the second metal interconnection and aninterconnection pattern were formed. A plasma CVD film for surfaceprotection was also formed. Lastly, annealing was performed in ahydrogen atmosphere at 400° C. FIG. 1 shows the degradationcharacteristics of a fine MOS transistor device formed through the aboveprocess.

FIG. 1 shows the substrate current (Isub) dependency per unit channelwidth of the reliability life time of the device. The substrate current(Isub) is directly proportional to the number of hot carriers generated;the larger the power supply applied to a device, the larger thesubstrate current. As shown in FIG. 1, there is a linear relationship,on a log-log plot, between the reliability life time and the substratecurrent (Isub) according to hot carriers. Hence, it is common practiceto use the substrate current dependency of characteristics degradationin order to predict the reliability life time. It is predicted from FIG.1 that the life time is about two months for a power supply of 3.3 V; inpractice, the life time is required to be 10 years. This demonstratesthat a device having such an interlevel film configuration cannot ensurea satisfactory reliability.

SUMMARY OF THE INVENTION

It is a principal object of the present invention to provide a highlyreliable semiconductor device in which interlevel films independent ofhot carriers are formed and planarization is achieved, and a method offabricating the same.

In order to achieve the above object according to an aspect of thepresent invention, there is provided a semiconductor device comprisingan interlevel film deposited by a first dielectrics film containingdangling bonds and a bonded group of Si and hydrogen, and a seconddielectrics film formed on the first dielectrics film.

According to another aspect of the present invention, there is provideda method of fabricating a semiconductor device, comprising the steps offorming a first dielectrics film containing dangling bonds and a bondedgroup of Si and hydrogen, and forming a second dielectrics film on thefirst dielectrics film, thereby forming an interlevel film.

According to still another aspect of the present invention, there isprovided a method of fabricating a semiconductor device, comprising thesteps of forming a semiconductor device and a first metalinterconnection on a semiconductor substrate, forming a firstdielectrics film containing dangling bonds and a bonded group of Si andhydrogen, and forming a second dielectrics film on the first dielectricsfilm, thereby forming an interlevel film.

According to still another aspect of the present invention, there isprovided a method of fabricating a semiconductor device, comprising thesteps of forming a first dielectrics film capable of suppressingpenetration of water on a semiconductor substrate, forming a seconddielectrics film by spin on glass or chemical vapor deposition, heatingthe semiconductor substrate to desorb all or part of water from thesecond dielectrics film, and forming a third dielectrics film so as notto expose the surface to an atmosphere containing a large amount ofwater, thereby forming an interlevel film constituted by the dielectricsfilms.

According to still another aspect of the present invention, there isprovided a method of fabricating a semiconductor device, comprising thesteps of forming a semiconductor device and a first metalinterconnection on a semiconductor substrate, forming a firstdielectrics film capable of preventing penetration of water, forming asecond dielectrics film on the first dielectrics film, forming a thirddielectrics film having different characteristics from those of thesecond dielectrics film, forming holes reaching the first metalinterconnection, and forming a second metal interconnection.

According to still another aspect of the present invention, there isprovided a method of fabricating a semiconductor device, comprising thesteps of forming a semiconductor device and a first metalinterconnection on a semiconductor substrate, forming a firstdielectrics film capable of suppressing penetration of water, forming asecond dielectrics film on the first dielectrics film, forming a thirddielectrics film having different characteristics from those of thesecond dielectrics film, forming a second metal interconnection on thethird dielectrics film, and forming holes reaching the first metalinterconnection, thereby connecting the first and second metalinterconnections.

According to still another aspect of the present invention, there isprovided a method of fabricating a semiconductor device, comprising thesteps of forming a silicon oxide film containing at least one of oxidesof boron and phosphorus on a semiconductor substrate on which asemiconductor device is formed, forming a first dielectrics filmcontaining dangling bonds and a bonded group of Si and hydrogen, andforming a second dielectrics film on the first dielectrics film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the life time characteristics of substratecurrent-gm degradation indicating the reliability life timecharacteristics of a device;

FIG. 2 is a sectional view showing the structure of one embodiment of asemiconductor device according to the present invention;

FIG. 3 is a graph showing the water content analysis results obtained bya TDS method for an SiO₂ film formed by ozone TEOS-SiO₂ film formed byECR plasma CVD;

FIG. 4 is a graph showing the water content analysis results obtained byusing the presence/absence of an ECR plasma CVD-SiO₂ film on an ozoneTEOS-SiO₂ film as a parameter;

FIG. 5 is a graph showing the reliability life time characteristics of adevice when the present invention is applied;

FIG. 6 is a sectional view showing the structure of a semiconductordevice according to another embodiment of the present invention;

FIG. 7 is a graph showing the degradation characteristics of the deviceshown in FIG. 6;

FIG. 8 is a graph showing the ESR spectrum of an ECR plasma CVD-SiO₂film;

FIG. 9 is a graph showing the reliability life time characteristics ofdevices using films listed in Table 1;

FIG. 10 is a graph showing an amount of dangling bonds in a dielectricsfilm formed by ECR plasma CVD;

FIG. 11 is a graph showing the hydrogen and water content analysisresults obtained by TDS (Thermal Desorption Spectroscopy) when SiO₂films having different film thicknesses are formed on SOG films by theECR plasma CVD;

FIG. 12 is a graph showing the water content analysis results obtainedby the TDS when an ECR plasma CVD film is formed on SOG and the gas flowratio of SiH₄ to oxygen is changed;

FIG. 13 is a graph showing the Si-H peak of the infrared absorptioncharacteristics of an ECR plasma CVD dielectrics film when a gas flowratio is changed;

FIG. 14 is a graph showing the water content desorption analysis resultobtained by the TDS for an SiO₂ film formed on SOG by the plasma CVD;

FIG. 15 is a graph showing the reliability life time characteristics ofa device when the present invention is applied;

FIG. 16 is a cross-sectional view showing the structure of amodification of the present invention;

FIGS. 17 and 18 are graphs showing the device degradationcharacteristics when various treatments are performed for interlevelfilms;

FIGS. 19, 20, and 21 are graphs showing the measurement results of watercontent thermal desorption spectra; and

FIGS. 22 and 23 are sectional views showing the structures ofmodifications of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiment 1

FIG. 2 shows one embodiment of a semiconductor device according to thepresent invention, particularly the section of a MOSFET. Referring toFIG. 2, reference numerals 1a and 1b denote oxide films for isolation;2, a gate electrode; 3, a gate oxide film; 4, a silicon substrate; 5a,5b, and 5c, first interlevel dielectrics; 6a and 6b, first metalinterconnections; 7 and 9, first (lowermost) and third (uppermost)interlevel films of a second interlevel dielectrics; 8, a second(intermediate) interlevel film of the second interlevel dielectrics; and10 and 11, source and drain regions formed in a semiconductor substrate.The gate electrode 2, the gate oxide film 3, the source region 10, andthe drain region 11 constitute a MOS transistor semiconductor device. Inthis embodiment, 3,000-Å thick polysilicon was formed as the gateelectrode 2, the gate oxide film 3 was formed to have a thickness of 100to 200 Å by dry oxidation, and 5,000-Å thick AlSiCu was formed as themetal interconnections 6a and 6b. As the first and third interlevelfilms 7 and 9, SiO₂ films were formed to have thicknesses of 3,000 Å and2,000 Å, respectively, by using ECR (Electron Cyclotron Resonance)plasma CVD (Chemical Vapor Deposition). As the second interlevel film 8,an ozone TEOS-SiO₂ film formed by atmospheric-pressure CVD takingadvantage of decomposition of TEOS in the presence of ozone was used.

The ECR plasma CVD is a method of forming high-quality dielectrics filmsat low temperatures of 200° C. or less. The film formation conditions inthis embodiment were a gas pressure of 1.0 mTorr of a gas mixture ofSiH₄ and O₃ and a microwave power of 600 W. In this embodiment, no rf(radio frequency) power is applied in an ECR plasma CVD system. However,it is naturally possible to apply the rf power in order to furtherimprove the film quality. In particular, the application of the rf poweris essential to improve step-height side walls.

The film formation conditions for the ozone TEOS-SiO₂ film were a flowrate of 3 l/min. of nitrogen gas flowed through TEOS kept at 65° C., anozone flow rate of 38 ml/min., and a substrate temperature of 400° C.

FIG. 3 shows the water content analysis results obtained by TDS (ThermalDesorption Spectroscopy) for the ozone TEOS-SiO₂ film and the SiO₂ filmformed by the ECR plasma CVD. Referring to FIG. 3, the temperature isplotted on the abscissa, and the ion intensity is plotted on theordinate. This graph reveals that the water content of the ozoneTEOS-SiO₂ film is much larger than that of the ECR plasma CVD-SiO₂ film.

FIG. 4, on the other hand, depicts the water content analysis resultsobtained by using the presence/absence of the ECR plasma CVD-SiO₂ filmon the ozone TEOS-SiO₂ film as a parameter. In FIG. 4, the temperatureis plotted on the abscissa, and the ion intensity is plotted on theordinate. As can be seen from FIG. 4, in characteristics curve acorresponding to the presence of the ECR plasma CVD-SiO₂ film, waterappears from 440° C.; in characteristics curve b corresponding to theabsence of the ECR plasma CVD-SiO₂ film, water appears from 70° C. Fromthis comparison, it will be understood that the dielectrics film formedby the ECR plasma CVD has a blocking effect against water.

FIG. 5 is a graph showing the reliability life time characteristics of adevice obtained when the present invention is applied. FIG. 5demonstrates the film thickness dependence of an ozone TEOS-SiO₂ filmand the results obtained when SiO₂ films were formed on and below theozone TEOS-SiO₂ film by the ECR plasma CVD. In this graph, the substratecurrent (Isub) is plotted on the abscissa, and the gm life time isplotted on the ordinate. The graph of FIG. 5 shows that the life time ofthe device decreases with the increasing film thickness of the ozoneTEOS-SiO₂ film. In particular, the life time was 62 days for a powersupply of 3.3 V when the film thickness was 1.0 μm (indicated by symbols◯ in FIG. 5); the device cannot be put into practical use. However, thelife time was remarkably improved (indicated by symbols ) by formingthe SiO₂ film below the 1.0-μm thick ozone TEOS-SiO₂ film by the ECRplasma CVD. The life time was improved because the SiO₂ film formed bythe ECR plasma CVD blocked the penetration of water from the ozoneTEOS-SiO₂ film to the device. The present invention, therefore, has acharacteristic that it provides an interlevel dielectrics filmconfiguration required for a multilevel interconnection and at the sametime ensures a high reliability of a device.

Note that the SiO₂ film according to the ECR plasma CVD used in thisembodiment can be a nitride film or an oxy-nitride-film, i.e., can beany film as long as the film can block water.

FIG. 6 shows the second embodiment of the present invention. FIG. 6 isidentical with FIG. 2 except for a portion of the second interlevel film8 shown in FIG. 2. A second interlevel film 8 shown in FIG. 6 is adielectrics film formed by a coating method. In this embodiment, an SOG(Spin On Glass) film is used as the dielectrics film according to thecoating method. FIG. 7 shows the reliability life time characteristicsof a device according to this embodiment. Referring to FIG. 7, thesubstrate current (Isub) is plotted on the abscissa, and the gm lifetime is plotted on the ordinate.

FIG. 7 is a graph showing the degradation characteristics of a deviceobtained when a 3,000-Å thick SiO₂ film is formed on a device by the ECRplasma CVD, a 3,000-Å thick SOG film is formed on the SiO₂ film, and a2,000-Å thick SiO₂ film is formed on the SOG film by the ECR plasma CVD.In this graph, the substrate current (Isub) is plotted on the abscissa,and the gm life time is plotted on the ordinate. FIG. 7 demonstratesthat the life time of the device at a power supply of 3.3 V is about 10year; the life time is of no problem. That is, in the present invention,a dielectrics film formed by the ECR plasma CVD has a blocking effectagainst water, and there can be provided an interlevel film formationmethod which assures a high reliability.

Embodiment 2

FIG. 8 shows an ESR (Electron Spin Resonance) spectrum of an ECR plasmaCVD-SiO₂ film. From this spectrum analysis, it is determined thatdangling bonds contained in the ECR plasma CVD-SiO₂ film are mainly Siatoms possessing unpaired electrons called E' centers. Table 1 shows thedependency of an unpaired electron density on deposition and annealingconditions measured by the ESR.

                  TABLE 1    ______________________________________                   Unpaired electron density    Conditions     (10.sup.18 spins/cm.sup.3)    ______________________________________    Immediately after                   19.0    deposition    After deposition    Nitrogen annealing at                   1.5    400° C. for 30 min.    Hydrogen annealing at                   0    400° C. for 30 min.    ______________________________________

Table 1 reveals that although the unpaired electron density can bedecreased by annealing, it can be almost perfectly eliminated by ahydrogen treatment. The water preventing effects were compared among thethree types of films listed in Table 1, i.e., the film containing alarge number of unpaired electrons, the film in which the number ofunpaired electrons was decreased by the nitrogen annealing, and the filmin which unpaired electrons were eliminated by the hydrogen annealing.The device structure and the interlevel dielectrics film configurationused in this evaluation were those shown in FIG. 2. Each of the abovethree types of ECR plasma CVD-SiO₂ films was deposited as the lowermostlayer to have a thickness of 0.3 μm, and a TEOS-O₃ film as anintermediate layer was deposited to have a thickness of 1.0 μm. Notethat an ECR plasma CVD-SiO₂ film was used as the uppermost layer.

FIG. 9 shows the reliability life time characteristics of the deviceshaving these film configurations. In this graph, the substrate current(Isub) is plotted on the abscissa, and the gm life time is plotted onthe ordinate. Referring to FIG. 9, symbols , Δ, and □ correspond to theECR plasma CVD film, the film subjected to the nitrogen annealing, andthe film subjected to the hydrogen annealing, respectively. Forcomparison, the characteristics obtained when no ECR plasma CVD-SiO₂film was used as the lowermost layer for water prevention are indicatedby symbols x, and the characteristics obtained when only the ECR plasmaCVD-SiO₂ film was used without using any TEOS-O₃ film as a watergeneration source are also illustrated. As is apparent from FIG. 9, whenno ECR plasma CVD-SiO₂ film for preventing water from the TEOS-O₃ filmwas used as the lowermost layer, the device life time was impracticallyshort. However, the device life time was prolonged by the use of thewater-preventing ECR plasma CVD-SiO₂ film, and this water-preventingeffect was enhanced as the unpaired electron density in the film wasincreased. The reason for this can be considered that water in the filmwas trapped by unpaired electrons. In this case, the characteristicsobtained are substantially the same as that when no TEOS-O₃ film as awater generation source was used, indicating that the ECR plasmaCVD-SiO₂ film functioned almost perfectly as a water-preventing film.

Note that when the SiH₄ /O₂ ratio of the material of the ECR plasmaCVD-SiO₂ film is changed over the range of 0.5 to 0.8, there is apossibility that a film having an SiH₄ /O₂ ratio of 0.5 or more can beused as a more effective water,preventing film. The dangling bond andwater preventing function of the ECR plasma CVD will be described below.

FIG. 10 illustrates an amount of dangling bonds in a dielectrics filmformed by the ECR plasma CVD, in which the gas flow ratio of SiH₄ tooxygen is plotted on the abscissa and the spin electron density, i.e.,the dangling bond density obtained by ESR measurement is plotted on theordinate. As can be seen from FIG. 10, the dangling bond density derivedfrom the ECR plasma CVD was 10¹⁸ cm⁻³ or more at a flow ratio of 0.5 ormore. When the flow rate of SiH₄ was decreased to reduce the gas flowratio, the spin electron density was smaller than the measurement limit.That is, dangling bonds are decreased in number when the gas flow ratiois reduced.

Embodiment 3

In this embodiment, an ozone TEOS-SiO₂ film was formed as anintermediate dielectrics film 8 of a second interlevel film byatmospheric-pressure CVD using decomposition of TEOS in the presence ofozone, and an SOG film was formed by spin on glass. An SiO₂ film having2,000 Å in thickness was formed as an uppermost dielectrics film 9 ofthe second interlevel film by plasma CVD. The film formation conditionsin this embodiment were a gas pressure of 1.0 mTorr of a gas mixture ofSiH₄ and O₂ and a microwave power of 600 W. After the SOG formation bythe spin on glass, curing was performed at 400° C. The ozone TEOS-SiO₂film and the SOG have high water absorption rates and therefore containlarge amounts of water.

FIG. 11 shows the hydrogen and water content analysis results obtainedby TDS (Thermal Desorption Spectroscopy) for structures in which SiO₂films having different film thicknesses are formed on SOG films by ECRplasma CVD. In this graph, the temperature is plotted on the abscissa,and the ion intensity is plotted on the ordinate. In the ECR plasma CVD,the gas flow ratio of SiH₄ to oxygen was 0.5. It is apparent from FIG.11 that the emission amount of hydrogen increased as the film thicknessincreased and emission of water started after the emission peak ofhydrogen.

FIG. 12 shows the water content analysis result obtained by the TDS foran SiO₂ film formed on SOG by the ECR plasma CVD while the gas flowratio of SiH₄ to oxygen is changed. In this graph, the temperature isplotted on the abscissa, and the ion intensity is plotted on theordinate. As can be seen from FIG. 12, the water-preventing effect wasimproved as the gas flow ratio was increased from 0.25 to 0.5, 0.7, and0.8.

FIG. 13 illustrates the Si-H peak of the infrared absorptioncharacteristics of a dielectrics film formed by the ECR plasma CVD whilethe gas flow ratio is changed. In this graph, the wave number is plottedon the abscissa, and the transmittance is plotted on the ordinate. FIG.13 reveals that Si-H bonds are increased with the increasing gas flowratio. Since the amount of dangling bonds in a film remains unchangedeven when the gas flow ratio is changed as demonstrated in FIG. 10,there is a possibility that bonded groups of Si and hydrogen in the filmare associated with production of dangling bonds. That is, it can beconsidered that not only dangling bonds but also Si-H bonded groupscontribute to the blocking effect against water of a dielectrics filmformed by the ECR plasma CVD. The characteristic of the presentinvention is to improve the water blocking by increasing the SiH₄ gasflow rate even in the ECR plasma CVD. It is, however, apparent from theabove examination that this effect can also be obtained by increasingSi-H bonds in an SiO₂ film by the use of Si₂ H₆ gas or by using anitride film or an oxy-nitride-film having Si-H bonds.

The formation of the uppermost dielectrics film 9 of the secondinterlevel film shown in FIG. 2 will be described. In the presentinvention, an SiO₂ film having 2,000 Å in thickness was formed as thedielectrics film 9 by using the plasma CVD for the reason explainedbelow. That is, when dielectrics films are to be formed by the plasmaCVD, since a wafer is heated up to 400° C. in a wafer holder of a plasmaCVD system, water can be desorbed from an intermediate dielectrics filmof the second interlevel film during a pre-treatment of the filmformation or during the film formation. In addition, the intermediatedielectrics film of the second interlevel film can be covered with theuppermost dielectrics film, so an interlevel film with little watercontent as a whole is realized.

FIG. 14 shows the water desorption analysis result obtained by the TDSfor an SiO₂ film formed on SOG by the plasma CVD. In this graph, thetemperature is plotted on the abscissa, and the ion intensity is plottedon the ordinate. It can be considered that since substrate heating at400° C. was performed in the plasma CVD, water in SOG disappeared duringthe heating up to 400° C., and no desorption peak appeared; this provesthe above assumption. Although the plasma CVD is adopted in the presentinvention, any thin film formation system having a substrate heatingmechanism can be used to realize this effect.

FIG. 15 shows the reliability life time characteristics of a deviceobtained when the present invention is applied, in which device SOG isformed on an ozone TEOS-SiO₂ film. In this graph, the substrate current(Isub) is plotted on the abscissa, and the gm life time is plotted onthe ordinate. It is apparent from this graph that the life time wasimproved when the power supply was 3.3 V. The life time was improvedbecause the lowermost dielectrics film blocked water and at the sametime water from the ozone TEOS-SiO₂ film and the SOG was desorbed duringformation of the uppermost dielectrics film, thereby reducing the watercontent in the films. The present invention has a characteristic that itcan provide an interlevel dielectrics film configuration required for amultilevel interconnection and can ensure a high reliability of adevice.

Embodiment 4

FIG. 16 shows a modification of the structure in FIG. 2, in which asecond metal interconnection 20 is formed on an uppermost dielectricsfilm 9 of a second interlevel film, and the lowermost dielectrics filmof a third interlevel film is formed on the layer 20. In this structure,as in the structure shown in FIG. 2, source and drain regions 10 and 11were formed on a semiconductor substrate 4, and a gate oxide film 3 anda gate electrode 2 were formed on a portion of the substrate sandwichedbetween the source and drain regions; these elements constituted a MOStransistor. First metal interconnections 6a and 6b were formed on thesource and drain regions through their respective contacts. A first(lowermost) dielectrics film 7, a second (intermediate) dielectrics film8, and the third (uppermost) dielectrics film 9 of the second interlevelfilm were formed in sequence on the metal interconnections 6a and 6b andon a dielectrics film 5c formed around the gate electrode. In thisconfiguration, the first interlevel dielectrics 5 consisted of aCVD-SiO₂ film and was annealed at 850° C. The metal interconnections 6aand 6b were formed after holes were formed in portions of the interlevelfilm 5 corresponding to the source and drain of the MOS transistor. Asthese metal interconnections, AlSiCu was formed to have a thickness of5,000 Å and patterned in accordance with a predetermined interconnectionpattern. The lowermost, intermediate, and uppermost dielectrics films 7,8, and 9 of the second interlevel film arranged on theseinterconnections were formed as follows. First, an SiO₂ film having3,000 Å in thickness was formed as the lowermost layer by ECR plasmaCVD, and an ozone TEOS-SiO₂ film was formed to have a thickness of 1,000Å to 3,000 Å. Subsequently, SOG to be combined with this ozone TEOS-SiO₂film to serve as the intermediate dielectrics film 8 was coated once andannealed in a nitrogen atmosphere at 400° C. for 30 minutes. Thereafter,an SiO₂ film was deposited to have a thickness of 1,000 Å as theuppermost dielectrics film by the ECR plasma CVD.

Holes (through holes) for connecting the first metal interconnectionswith the second metal interconnection 20 formed on them were formed indesired positions of the interlevel dielectrics 7, 8, and 9 on the firstmetal interconnections. Various treatments were performed as annealingafter the formation of the through holes, and the second metalinterconnection 20 was deposited and formed into a predeterminedinterconnection pattern. In addition, a plasma CVD film 21 for surfaceprotection was formed on the interconnection 20. In this case, thevarious treatments included: 1 annealing in a nearly vacuum atmosphere(with 100 cc of a nitrogen flow and a vacuum degree of 0.01 Torr orless) at 400° C. for 30 minutes; 2 annealing in a low-pressure (1/3 atm)nitrogen atmosphere at 400° C. for 30 minutes; 3 annealing in alow-pressure (1/3 arm) hydrogen atmosphere at 400° C. for 30 minutes; 4annealing in an atmospheric-pressure nitrogen atmosphere at 400° C. for30 minutes; and 5 no annealing. The above treatments in the vacuum,hydrogen, nitrogen atmospheres were performed for 30 minutes after thetemperature was stabilized.

FIG. 17 shows the degradation characteristics of fine MOS transistordevices with a channel length of 0.5 μm formed by processes includingthe above treatments. In this graph, the substrate current (Isub) isplotted on the abscissa, and the gm life time is plotted on theordinate. FIG. 17 shows the variation life time of a transconductance gmas representative characteristics of a MOS transistor. A thresholdvoltage as another representative device characteristics of the MOStransistor also exhibit a similar change but has a slightly longer lifetime in device characteristics. For example, the life time of thetransconductance gm at a gate voltage of 3.3 V is prolonged about 100times (about 9×10⁶ minutes) that obtained under the conventionalcondition of 5 no annealing, by performing 1 annealing in a vacuum at400° C. for 30 minutes. Although this effect is slightly decreased underthe condition of 2 annealing in a low-pressure (1/3 arm) nitrogenatmosphere, the gm life time is prolonged about 45 times (about 4×10⁶minutes). Under the condition of 3 annealing in a low-pressure (1/3 atm)hydrogen atmosphere, the gm life time is prolonged about 25 times (about2.5×10⁶ minutes) even though the effect is smaller than that obtained bynitrogen. When 4 annealing in an atmospheric-pressure nitrogenatmosphere is performed, the gm life time is prolonged about seven times(7×10⁵ minutes).

This phenomenon demonstrates that water contained in the ozone TEOS-SiO₂film and the SOG film was desorbed through the uppermost plasma CVD filmupon annealing. The effect decreased in an order of 1, 2, 3, and 4because the partial pressure (the pressure of water or vapor alone) ofwater in the atmosphere on the surface upon annealing changed. That is,under the condition of 1 annealing in a vacuum, exhaustion was performedat a maximum exhaust rate by a vacuum pump, so water on the substratesurface was exhausted immediately after desorbed from the substrate.Under the condition of 2 annealing in a low-pressure (1/3 atm) nitrogenatmosphere, on the other hand, the exhaust rate was decreased tomaintain the pressure at 1/3 atm. Therefore, the flow rate of nitrogengas on the substrate surface was low, and desorbed water more or lessstayed on the surface. For this reason, desorption of water from thesubstrate surface was determined by equilibrium between the atmosphereand the water, and this decreased the desorption rate of water from thesurface. In fact, when annealing was performed in the same vacuumatmosphere as the condition 1 but at the same exhaust rate as the1/3-atm nitrogen annealing by decreasing the flow rate of nitrogen gasto almost zero, nearly the same improving effect as the condition 2 wasobtained. This is so because the exhaust rates were almost the same. Inthe annealing in an atmospheric-pressure nitrogen atmosphere, since thegas flow rate on the substrate surface was lower than that in alow-pressure atmosphere, the water desorption rate was also lower. Theeffect of the hydrogen atmosphere was smaller than that of the nitrogenatmosphere at the same pressure because the water concentration thatnitrogen gas itself possesses is lower than that of hydrogen gas. Thewater concentration of nitrogen used in the above experiments was 10ppb.

As is apparent from the above results, the annealing in a nitrogenatmosphere performed after the formation of through holes has an effectof prolonging the variation life time of device characteristics of a MOStransistor. It is obvious that the same effect can be obtained even whenthis annealing process is performed not after the formation of throughholes but after the interlevel film formation process. In addition, theannealing in a low-pressure atmosphere remarkably enhances the effect ofprolonging the variation life time of device characteristics of a MOStransistor, and the effect is further enhanced in a vacuum atmosphere.Note that it is necessary to sufficiently exhaust water desorbed fromthe surface of a wafer. That is, a more startling effect can be obtainedby decreasing the water pressure in an atmosphere on the wafer surfaceas low as possible during annealing.

Embodiment 5

It was confirmed that when the annealing of the present inventiondescribed above in Embodiment 4 was performed not after the formation ofthrough holes but after the formation of the second metalinterconnection pattern 20 after the through hole formation, it waspossible to obtain an effect better than that obtained by the annealingafter the through hole formation.

The most significant effect can be obtained when, of course, theannealing is performed after both the formation of through holes and theformation of the second metal interconnection pattern 20.

In addition, when a plasma CVD film formed using TEOS and oxygen asreaction gases is used as the uppermost plasma CVD film, the diffusionrate of water is increased. Hence, water contained in the ozoneTEOS-SiO₂ film and the SOG film is desorbed more easily through theuppermost layer upon annealing after the formation of the interlevelfilms. This decreases an amount of water diffusing toward the substrateto suppress degradation caused by hot carriers.

Embodiment 6

In the above Embodiments 4 and 5, annealing is performed before or afterthe formation of the second interconnection. However, when a largernumber of interconnections, e.g., three or four interconnections are tobe formed, it is more preferable to perform the annealing processdescribed in the above embodiments each time the interconnection isformed.

Embodiment 7

As the second interlevel dielectrics in the structure shown in FIG. 2,an ECR plasma CVD-SiO₂ film 7, an ozone TEOS-SiO₂ film, and an SOG 8 asa coating film were annealed in a nitrogen atmosphere at 400° C., and anSiO₂ film 9 was deposited to have a thickness of 2,000 Å as an uppermostdielectrics film by TEOS plasma CVD in which film deposition wasperformed at a temperature of 400° C. For comparison, a sample was alsomanufactured in which a 2,000-Å thick film was formed as the uppermostfilm by ECR plasma CVD which deposited at room temperature.

Holes (through holes) for connecting a first metal interconnection witha second metal interconnection to be formed on the first metalinterconnection were formed in predetermined positions of the aboveinterlevel dielectrics on the first metal interconnection. After thesecond metal was deposited, an interconnection pattern was formed. Inaddition, as a passivation film, an ECR plasma CVD film was deposited tohave a thickness of 5,000 Å and annealed in a hydrogen atmosphere at400° C. for 30 minutes. Thereafter, the characteristics of the resultingMOS transistor were measured.

FIG. 18 shows the degradation characteristics of the MOS transistor witha channel length of 0.5 μm formed by the above process. In this graph,the substrate current (Isub) is plotted on the abscissa, and the gm lifetime is plotted on the ordinate. FIG. 18 illustrates the variation lifetime of a transconductance gm as representative characteristics of a MOStransistor. A threshold voltage as another representative devicecharacteristics of the MOS transistor also exhibit a similar change buthas a slightly longer life time in device characteristics. As shown inFIG. 18, the life time of gm obtained by using the TEOS plasma CVD-SiO₂film as the uppermost layer of the interlevel film is about ten timeslonger than that obtained by using the ECR plasma CVD-SiO₂ film. Thisresults from the difference in film formation conditions between theTEOS plasma CVD-SiO₂ film and the ECR plasma CVD-SiO₂ film; film isdeposited at nearly room temperature in the ECR plasma CVD, whereas itis started after a substrate is left to stand in a vacuum at atemperature of 400° C. for a few seconds to a few tens of seconds in theTEOS plasma CVD. This means that in the TEOS plasma CVD, annealing isperformed in a vacuum at a temperature of 400° C.; water is desorbedfrom SOG and the ozone TEOS-SiO₂ film during this annealing, and theTEOS plasma SiO₂ film is formed after that. In addition, the substrateis kept at a temperature of 400° C. during the film formation, so wateris desorbed through the formed thin film. Therefore, water in the SOGand the ozone TEOS CVD film is desorbed by these two effects. An ECRplasma CVD-SiO₂ film and a TEOS plasma CVD-SiO₂ film were actuallyformed on SOG films formed under the same conditions, and water thermaldesorption spectra (TDS) of these structures were measured. FIG. 19 is agraph showing the measurement results. Since the water content in theECR plasma CVD film or the TEOS plasma CVD film is very small comparedto that in the SOG film, it can be considered that water is desorbedmostly from the underlying SOG film. As is apparent from FIG. 19, thetotal amount of desorbed water from the TEOS plasma CVD film is muchsmaller than that from the ECR film. In particular, an amount of waterdesorbed near 400° C. is very small. The reason for this can beconsidered that since the film formation temperature of the TEOS plasmaCVD is 400° C., water desorbed at temperatures of about 400° C. or lessis removed effectively in the TEOS plasma CVD, and there is no largedifference in amount of water desorbed at higher temperatures betweenthe two processes. (It should be noted that the temperature is raised ata predetermined rate of 20° C./min. in the TDS measurement, so theresults are independent of the effect of annealing time. In practice,since the annealing is performed for 30 minutes, water desorbed attemperatures higher than 400° C. found in the TDS measurement is alsoremoved). The temperature does not largely exceed 400° C. so often in anormal interconnection formation process. Therefore, water desorbed at400° C. or more is unlikely to diffuse during the process to reach thegate oxide film of a MOS transistor, thereby eliminating adverseinfluences on the structure. That is, water desorbed at temperaturesnear 400° C. or less has a large influence, and FIG. 19 reveals that aconsiderable amount of water with this large influence is desorbedduring the formation of the TEOS plasma CVD film. In the graph of FIG.19, the temperature is plotted on the abscissa, and the water desorptionintensity is plotted on the ordinate. This is the reason why the lifetime of the transconductance gm of the structure using the TEOS plasmaCVD-SiO₂ film is larger than that of the structure using the ECR plasmaCVD-SiO₂ film, as shown in FIG. 18. In this embodiment, the descriptionhas been made by taking only the TEOS plasma CVD film as an example.However, the same effect can be obtained by forming a film by plasma CVDusing silane gas and N₂ O gas as reaction gases, which is performed atthe same film formation temperature of about 400° C.

It should also be noted that the above effect becomes useless if theuppermost TEOS plasma CVD film absorbs water from the atmosphere afterthe film formation. FIGS. 20 and 21 show the results of examination ofthis possibility. In each graph, the temperature is plotted on theabscissa, and the water desorption intensity is plotted on the ordinate.FIGS. 20 and 21 illustrate the measurement results of thermal desorptionspectra of samples formed by depositing 1,000-Å and 2,000-Å thick TEOSplasma CVD films on SOG films, respectively. Each graph also shows dataof TDS of a sample annealed in a nitrogen atmosphere at 400° C. for 30minutes after the film formation; one TDS measurement result wasobtained by placing the sample in a vacuum atmosphere for TDSmeasurement within one hour after the annealing, and the other TDSmeasurement result was obtained after the same sample was left to standin the air for two weeks. From comparison between the data obtainedafter the annealing, the water desorption intensity near 300° C. to 500°C. is slightly high in the sample left to stand for two weeks. However,it can be considered that the amount is not so large when this longperiod of two weeks is taken into account. In the sample having theuppermost TEOS plasma CVD film with a thickness of 2,000 Å, an increasein water content is very small. Hence, when the film thickness is 1,000Å or more, reabsorption of water is not a problem insofar as the TEOSplasma CVD-SiO₂ film is concerned.

In situations where this very small increase in water is of a problem, athin ECR plasma CVD-SiO₂ film or a thin silicon nitride film need onlybe formed on this TEOS plasma CVD-SiO₂ film.

The effect of removing water by desorption by increasing the substratetemperature up to about 400° C. during the formation of the aboveuppermost film is obtained because an ECR plasma CVD film having a lowwater permeability is formed to have a thickness of 3,000 Å below theSOG film and the ozone TEOS-CVD film. If such an underlying film is notformed or an underlying film with a high water permeability is formed,water diffuses into the MOS device region through the underlying filmduring heating of the substrate in formation of the uppermost film,causing degradation in characteristics. Therefore, it is necessary touse the ECR plasma CVD film or the like having a high ability to preventwater penetration. A film having this function may be a silicon nitridefilm (formable by plasma CVD or thermal decomposition CVD).

In this embodiment, 400° C. is exemplified as the substrate heatingtemperature in the formation of the uppermost film of the interlevelfilm. However, the higher the temperature, the better the resultingeffect. In an actual process, the temperature is about 300° C. to 500°C.

Embodiment 8

The effect of the above Embodiment 7 cannot necessarily be obtainedunless the substrate is heated to about 400° C. during film formation.The same effect can be obtained by performing annealing at a hightemperature before a film is formed on an SOG film and an ozoneTEOS-CVD-SiO₂ film and then forming a film on it in a condition in whichno water is absorbed by the structure. That is, the SOG film and theozone TEOS-CVD film absorb water in a few minutes when exposed to theair. Therefore, film formation need only be performed by transferringthe substrate from an annealing system to a plasma CVD system through avacuum atmosphere or a nitrogen or argon atmosphere containing littlewater. In this case, as already described above in the Embodiment 7, theplasma CVD film formed must be a film which does not absorb water in theatmosphere or in an aqueous solution in the subsequent processes afterthe film formation. A TEOS plasma CVD-SiO₂ film or an ECR plasmaCVD-SiO₂ film as described above is satisfactory for this purpose. Sincethe ECR plasma CVD film allows almost no penetration of water when leftto stand at room temperature, this film is stronger than the TEOS plasmaCVD films shown in FIGS. 20 and 21 against being left to stand after theannealing.

Embodiment 9

In order to further enhance the effect of removing water by desorptionof the above Embodiments 7 and 8, a process of performing annealing at atemperature of about 400° C. may be introduced after formation of aninterlevel film. As is apparent from FIGS. 20 and 21, even when filmformation is performed at 400° C., if annealing is performed at 400° C.for 30 minutes after that, an amount of water desorbed at a temperatureof about 400° C. to 500° C. is greatly reduced. This indicates thatwater was again desorbed through a TEOS plasma CVD film by the annealingat 400° C. for 30 minutes; the effect of the annealing is significant.It should be noted, however, that the annealing also encouragesdiffusion of water into the underlying MOS device region. Therefore, inorder to effectively desorb water during the annealing process, it isrequired that a film having a high ability to prevent penetration ofwater, such as an ECR plasma CVD film or a silicon nitride film(formable by plasma CVD or thermal decomposition CVD), be formed belowthe SOG and the ozone TEOS-CVD film of an interlevel film. It is alsonecessary that the film to be formed on that film must have a higherwater permeability than that of the underlying film. In this case, thisuppermost film must have an ability to prevent penetration of water attemperatures near room temperature. In addition, the film thickness ofthe uppermost film is preferably as small as possible provided that thefilm does not lose its water penetration preventing function at aboutroom temperature. The water permeability of the uppermost film of theinterlevel film need not be higher than that of the underlying film overthe full temperature range but need only be higher than that over therange of 300° C. to 500° C. centered on 400° C. as the highesttemperature in the interconnection process. Examples of such a film area TEOS plasma CVD film when the underlying film is an ECR plasma CVDfilm, and a TEOS plasma CVD film, an ECR plasma CVD film, or asilane-based plasma CVD film when the underlying film is a siliconnitride film.

The annealing process need only be performed after the uppermost film ofthe second interlevel film is formed and before the film having a lowwater permeability is formed on that film. In a regular MOSLSIinterconnection process, therefore, the annealing is performedimmediately after formation of the second interlevel film, after throughholes are formed in the second interlevel film in order to connect thesecond interlevel film with the upper second metal interconnection, orafter formation of the second metal interconnection pattern after that.

It is also possible to obtain the water removing effect by desorbingwater from the interlevel films during the annealing process withoutperforming the water removing process shown in Embodiments 7 and 8.

In addition, as the annealing temperature is increased, the waterdiffusion rate is also increased, and a better effect results in.

Embodiment 10

In a semiconductor integrated circuit including a MOS transistor, asshown in FIG. 22, phosphorus-doped polysilicon as a gate electrode 2 wasformed on a gate oxide film 3, CVD-SiO₂ films 5a, 5b, and 5c containingan oxide of boron (B) or phosphorus (P) were formed as a firstinterlevel film, and annealing was performed at 800° C. to 1,000° C. Oneimportant role of this oxide film is to decrease, by formation of thesmooth surface interlevel film, a step height produced by formation ofthe underlying gate electrode and the like. In particular, a siliconoxide film containing B or P acquires flowability upon annealing at 800°C. to 1,000° C. to yield a smooth film. Another important role isderived from the ability of the oxide of B or P contained in this filmto trap and inactivate mobile ions, such as Na, having a very bad effecton characteristics of a MOS transistor. The use of the film having thiseffect as the first interlevel films 5a, 5b, and 5c not only preventspenetration of mobile ions, such as Na, from the upper layer but alsoabsorbs mobile ions, such as Na, which have penetrated into the MOSdevice region below this film during the device formation process,thereby protecting the device against contamination by mobile ions. Inaddition, as shown in FIG. 23, a film 40 having a high ability toprevent water penetration, such as an ECR plasma CVD film using electroncyclotron resonance or a silicon oxide film (formable by plasma CVD orthermal decomposition CVD), is deposited on the first interlevel film.Therefore, when first metal interconnection patterns 6a and 6b areformed on the film 40 and a film consisting of, e.g., an SOG film and anozone TEOS-CVD film is formed as a second interlevel dielectrics 8, theabove film 40 can prevent penetration of water from the dielectrics film8 into the underlying device. Note that reference numeral 20 denotes asecond metal interconnection connected with the first metalinterconnection 6a via through holes as in the structure shown in FIG.16.

As a simple arrangement for preventing degradation with time of a MOStransistor caused by hot carriers, it is possible to form a film havinga high ability to prevent water penetration, such as the silicon nitridefilms 5a, 5b, and 5c, immediately above the MOS transistor, form aCVD-SiO₂ film containing at least one of oxides of boron (B) andphosphorus (P) on that film, and perform annealing at 800° C. to 1,000°C. However, when the silicon nitride films 5a, 5b, and 5c are formedimmediately above the MOS transistor, diffusion of mobile ions, such asNa, which have penetrated during the process of forming the underlyingdevice is also suppressed; this is unpreferable in terms of protectionof the device against mobile ions. Therefore, it is preferable to formthe film 40 having a low water permeability, such as a silicon nitridefilm, after formation of the CVD-SiO₂ film containing an oxide of B orP, as the interlevel film.

Embodiment 11

In the above Embodiment 10, after formation of the CVD-SiO₂ filmcontaining at least one of oxides of boron (B) and phosphorus (P) as thefirst interlevel film, the film having a high ability to preventpenetration of water, such as a silicon nitride film, is formed, andthen the first metal interconnection is formed on it. However, theconfiguration is not necessarily this one. That is, a CVD-SiO₂ filmcontaining at least one of oxides of B and P need only be formed belowthe silicon oxide film or the like. Therefore, as shown in FIG. 23,after a film 43 capable of preventing water penetration, such as asilicon nitride film, is formed on a CVD-SiO₂ film 42 containing atleast one of oxides of B and P, a CVD-SiO₂ film 8 containing at leastone of oxides of B and P may be formed. Although annealing at 800° C. to1,000° C. may be performed after formation of each CVD-SO₂ film, it needonly be performed after formation of the second film 8. In thisconfiguration, the function of trapping mobile ions, such as Na, whichhave penetrated during the device formation process is assigned to thelower film, and the function of obtaining an underlying planarizingstructure for forming a metal interconnection on it and the function oftrapping mobile ions from the upper portion are assigned to the upperfilm.

In addition, when a silicon nitride film having a very high ability toprevent water penetration is used in the structure, a high flowabilitycan be obtained at a low annealing temperature of 750° C. to 900° C. ifannealing is performed in an atmosphere containing a large quantity ofwater vapor after the formation of the upper CVD-SiO₂ film containing atleast one of oxides of B and P. The result is a smooth, planarizedsurface profile. The low-temperature annealing is advantageous as aprocess of forming a miniaturized device in that diffusion of dopedimpurities can be suppressed. If this annealing in a water vaporatmosphere is performed without the intermediate silicon nitride film,water diffuses to the device region to induce oxidation of the substrateor the gate polysilicon, thereby adversely affecting the device. Withthe use of the intermediate silicon nitride film, the influence on theunderlying device is reduced and a smooth surface profile can beobtained because of a low annealing temperature. The film thickness ofthe silicon nitride film need only be 100 Å. Although it depends on thefilm formation method, a film thickness of 50 Å cannot satisfactorilyprevent water penetration.

As has been described above in detail, the present invention can achievethe effects summarized below.

1 According to the characteristics features of the present invention, adielectrics film capable of preventing penetration of water, such as anSiO₂ film formable by ECR plasma CVD or a silicon nitride film, isformed below a metal interconnection. Therefore, even when a dielectricsfilm containing a large amount of water is formed as a metalinterconnection interlevel film on the metal interconnection by spin onglass or ozone TEOS-CVD, water diffusion toward the underlying layer canbe suppressed. As a result, it is possible to form an interlevel filmwhich does not degrade a device.

2 According to the characteristics features of the present invention, asan interlevel film between metal interconnections, a dielectrics filmcapable of preventing penetration of water, such as an SiO₂ filmformable by ECR plasma CVD or a silicon nitride film, is formed below adielectrics film formed by spin on glass or ozone TEOS-CVD. An upperplasma CVD film is formed while water is desorbed, or immediately afterdesorption of water, in a condition that reabsorption of water isprevented, or water is desorbed away effectively by performing annealingafter the formation of the interlevel film, thereby decreasing the watercontent in the interlevel dielectrics. Therefore, it is possible to forman interlevel film which does not cause degradation in a device.

3 According to the characteristics features of the present invention, adielectrics film containing dangling bonds and Si-H is formed below atleast a dielectrics film formed by spin on glass or ozone TEOS-CVD,thereby blocking water from the dielectrics film. In addition, anotherdielectrics film is formed on the above dielectrics film, formed by thespin on glass or the ozone TEOS-CVD, by using a dielectrics filmformation system while a substrate is heated. As a result, there isprovided an interlevel film without giving any hot carrier degradationto a device.

What is claimed is:
 1. A method of fabricating a semiconductor device,comprising the steps of:forming a first dielectrics film capable ofsuppressing penetration of water on a semiconductor substrate; forming asecond dielectrics film by spin on glass or chemical vapor deposition;heating said semiconductor substrate to desorb all or part of water fromsaid second dielectrics film; and forming a third dielectrics film in anatmosphere substantially free of water, thereby forming an interlevelfilm constituted by said dielectrics films.
 2. A method of fabricating asemiconductor device, comprising the steps of:forming a semiconductordevice and a first metal interconnection on a semiconductor substrate;forming a first dielectric film containing dangling bonds and a bondedgroup of Si and hydrogen; forming a second dielectric film on said firstdielectric film; forming a third dielectric film having differentcharacteristics from said second dielectric film on said seconddielectric film, thereby forming an interlevel film constituted by saiddielectric films.
 3. A method according to claim 2, wherein said thirddielectrics film is formed while water is desorbed from said seconddielectrics film.
 4. A method according to claim 1, wherein said firstdielectrics film is formed by ECR plasma CVD.
 5. A method according toclaim 4, wherein said first dielectrics film is a silicon oxide film. 6.A method according to claim 1, wherein said first dielectrics film is anitride film.
 7. A method of fabricating a semiconductor device,comprising the steps of:forming a semiconductor device and a first metalinterconnection on a semiconductor substrate; forming a firstdielectrics film capable of preventing penetration of water; forming asecond dielectrics film on said first dielectrics film; forming a thirddielectrics film having different characteristics from those of saidsecond dielectrics film; forming holes reaching said first metalinterconnection; and forming a second metal interconnection.
 8. A methodaccording to claim 7, wherein annealing is performed after formation ofsaid holes reaching said first metal interconnection.
 9. A methodaccording to claim 7, wherein said first dielectrics film is formed byECR plasma CVD.
 10. A method according to claim 9, wherein said firstdielectrics film is a silicon oxide film.
 11. A method according toclaim 7, wherein said first dielectrics film is a nitride film.
 12. Amethod of fabricating a semiconductor device, comprising the stepsof:forming a semiconductor device and a first metal interconnection on asemiconductor substrate; forming a first dielectrics film capable ofsuppressing penetration of water; forming a second dielectrics film onsaid first dielectrics film; forming a third dielectrics film havingdifferent characteristics from those of said second dielectrics film;forming a second metal interconnection on said third dielectrics film;and forming holes reaching said first metal interconnection, therebyconnecting said first and second metal interconnections.
 13. A methodaccording to claim 12, wherein said first dielectrics film is formed byECR plasma CVD.
 14. A method according to claim 13, wherein said firstdielectrics film is a silicon oxide film.
 15. A method according toclaim 12, wherein said first dielectrics film is a nitride film.